Nanomaterials are particles having a size of from 1 to 30 nanometers in diameter. Use of nanomaterials have been known in rubber. For example, in U.S. Pat. No. 4,644,988, there is disclosed a tire tread compound containing a styrene-butadiene copolymer rubber reinforced with a high structure carbon black designated as N103 and a particle size smaller than 20 nanometers. In addition, it is known from U.S. Pat. No. 4,474,908 that siliceous fillers having an ultimate particle size in the range of from 15 to 30 nanometers have been used in rubber. One advantage in using such nanomaterials in rubber is to improve the treadwear. Unfortunately, upon mixing nanomaterials in a rubber composition, such nanomaterials tend to reagglomerate and, therefore, increase the individual particle sizes which result in decreasing the benefits for which they are added. In addition, with increasing levels of nanomaterials in place of larger particles (&gt;100 nanometers in diameter), the rubber becomes more hysteretic.
Japanese Unexamined Patent 8-133720 discloses a production method of precipitated silica granulate involving (a) mixing 100 percent of precipitated silica powder, in which a mean particle size is more than 60 .mu.m and a particle hardness is 10-30 g, with 5 to 30 percent of precipitated silica powder, in which a mean particle size is less than 20 .mu.m, and (b) granulating.